1. Field of the Invention
The present invention relates generally to a diagnosing apparatus which is used in a vehicle control system wherein signals are supplied from sensors to a microcomputer to control the driving of actuators, and which diagnoses malfunction of the control system using the microcomputer.
2. Description of the Related Art
There is known a diagnosing apparatus which performs self-diagnosis according to previously installed programs while a vehicle is running under normal conditions, and turns on an alarm lamp when detecting the malfunction to indicate where the malfunction takes place. The diagnosis of this apparatus, however, may not be completely reliable. When a vehicle is driven in various modes (driving conditions), this apparatus may not properly diagnose the occurrence of a malfunction even if it has occurred, or may erroneously diagnose the occurrence of a malfunction even if it has not occurred. When vehicles are diagnosed by qualified people, e.g., dealers, repairers, etc., the vehicles are driven in a predetermined mode to prevent erroneous diagnosis, or even the same diagnosing items may be checked by different methods to improve the precision of self-diagnosis. In other words, the self-diagnosis is carried out in repair shops in accordance with a special program newly prepared for this purpose.
The technique that relates to an apparatus which executes self-diagnosis in accordance with such two types of programs is disclosed in, for example, Japanese Unexamined Patent Publication No. 62-188933. This scheme uses a first program which is run in normal mode (first mode) and a second program which is run in check mode (second mode) at a higher detection precision than the first program. When a user drives a vehicle, the normal mode is selected and self-diagnosis is executed in accordance with the first program. At the time a vehicle is inspected or is repaired in a repair shop, the check mode is selected and self-diagnosis is executed in accordance with the second program.
The mode selection is performed based on the status of a test switch (test terminal) provided in the vehicle or the engine room and the status of the ignition switch. For example, the check mode (second mode) is selected in a repair shop when the ignition switch is set on and the test switch is closed, and the normal mode (first mode) is selected otherwise.
If a vehicle is returned to the user without releasing the check mode (first mode), i.e., without setting the test switch off after diagnosis in the repair shop is completed, the following problem arises. Even when a slight malfunction occurs while the user is driving the vehicle under the normal conditions, i.e., even when an instantaneous malfunction which hardly affects the driving occurs, such an event is diagnosed as a malfunction and the alarm lamp is lit. This is likely to make the user overanxious.